Inborn errors of metabolism (IEM) are a group of rare genetic (inherited) disorders that cause a block in a metabolic pathway leading to clinically significant consequences, causing developmental and intellectual disabilities, seizures, and, if untreated, coma and death. The majority of the IEM disorders are managed by manipulation and modification of diet alone to reduce toxic metabolites, or with a combination of dietary modification and medications. The complex dietary therapies used in IEM challenge routine dietary recommendations and render diet apps designed for the general public of little utility in these conditions. Also, no diet app is developed specifically for the IEM community and meets the rigor required for research, particularly the need to measure specific and multiple amino acid content in the diet to facilitate more study on impact on brain neurochemistry. Within the field of IEM, the use of three-day diet diaries is utilized to monitor food intake. These diaries are frequently inadequate in capturing what is actually being consumed due to recall errors and other factors. Novel methods of assessing dietary intake and making individualized dietary recommendations for people with IEM are required to reduce the diet tracking burden and to improve the adequacy of dietary recommendations. We propose to develop and validate MyRareDiet to address an unmet need in the IEM population to assist with dietary management designed to increase adherence and compliance that leads to improved outcomes, while facilitating the collection of dietary data from individuals with IEM for research purposes. MyRareDiet includes a Patient Portal, a Clinical Dietician Portal, and a Researcher Portal. The Patient Portal is to help IEM patients track and monitor their own diet so they can meet their strict diet targets and restrictions. The Clinical Dietician Portal is to help clinical dieticians manage diet modifications for individuals with IEM. The Researcher Portal is to facilitate the conduct of diet-based studies and the analysis of study results. The aims for Phase I are: 1) Collect stakeholder feedback from stakeholders, including IEM patients/caregivers, dietitians, and researchers via focus groups; 2) Develop the prototype MyRareDiet system using user-centered design and the latest mobile-enabled e-technologies; 3) Conduct prototype evaluation including usability and usefulness tests and validation study comparing patient/caregiver-recorded diets using MyRareDiet and those recorded by nutrition students interviewing patients/caregivers with another diet recording tool. Our success criteria are based on evaluations on system usability (>=77.8), perceived usefulness (>=4), and the agreement (> 90%) of diets recorded by patients/caregivers and those by nutrition students.